Telephone system



July 2', 1935- H. HOVLAND 2,006,354

TELEPHONE SYSTEM Filed June 20,' 19.3 4 2 Slxees-Sheel'l l lofr# kom Rr srEP MA RGINA L e y Yl/vl/.E/vrfe l #Hol/LAND @V7/QW ATTORNEY Ju-ly. 2, 1935.` H HOVLAND 2,006,354

TELEPHONE SYSTEM Filed Junezo, 1934 2 sheets-sheet 2 Vlg ' ArokNEr Patentedr July Z, '1935 i UNITED f STATES PATENT OFFICE 1 o l n 2,006,354 t a 'rELEPHONE.,Sarsfielu K k Henry Hovland, Williston `Ifarloll., Y., assigner to Bell y'Ieleplnme Laboratories, Incorporated; New York,zN. Y., a corporation of New York ,',Appiicativnn June 2o, 1934, serial No. 731,432

i 1o*o1aims. c1. 17e-enz.)l l

cuit isfclosedv assoon as the testbrush engages This invention relates to telephone systems and more particularlyto systems employing automatic switches ofthe step-by-step type.

Thepobject of' theinvention .1s to provide a g 5 circuitf'arrangement for stepfby-step ,switches which is more reliable in operation and which.v is capable ofsatisfactory operation when asso-l ciated with lines or` trunks which have'a lower conductivity or a lower insulation resistance than has heretofore beenfound practicable. A further object of theinvention is to provide a circuit arrangement in which the possibility of a trunk being-simultaneously seized by two switches is eliminated. a r l Y r According to this invention a circuit arrangel:ment is provided for a switch ofv the step-by-'step typewhereinA a holding circuit is closed for the kstepping magnet as soonas the shaft and brushes begin to move out of one position until the next position is reached, thereby continuing the en- -gagement of the stepping pawl with'the ratchet long enough to prevent overstepping.-

yA feature of the'nvention fis` a two-motion i' step-by-'step'switch in :which contact springs are actuated bythe movementl of the double dog at the beginning ofthe movement of the shaft out of any of its vertical positions of rest, thereby lclosing a holding circuit for thevertical-stepping magnet to insure the engagement `of the verticalstepping pawl with the vertical ratchetfor a long `enough,interval to prevent overstepping. If the switch isdirectivelyoperated in its rotary movement, the closing of the, double dog springs at the beginningof each rotary step is effective to hold the rotary-steppingv magnet operated and vthereby insure the engagement of the rotarystepping pawl with the rotary ratchet long enough to prevent overstepping. y f

A further feature of the inventionis a new and reliable circuit arrangement for a step-by-stfep f selector switch wherein the brushes rare advanced Vduring trunk-hunting until the testk brushl encounters a batterypotential, suicient resistance being'included in the idle battery connection 'to insure against the seizure ,of thev same trunk by two selectors at Athesaine time. According to one' embodiment yofthis feature, a back contact and one winding of a differentially wound stepping relay are included in the test circuit, whereby the test circuitis closed as soon as the stepping relay releasesV and without danger otk overstepping. According to an'alternative embodiment of this f feature, the test circuit includes a continuity contact of the'stepping vmagnet andthe winding rof a marginal Steppingrelay whereby "the test, `cirment for a selector.

a tooth of the vertical` or rotary ratchets.

the test terminal of each set to which the selector brushes are advanced. t The drawings which form a part of this specinot limited in its application to arrangements shown.

- Referring to the drawings,

Fig. 1 shows, schematically, subscribers sta-,- tions rA and B, a lineender LFI, a selector Si., and a connector C; n f

Fig. 2 shows an alternative circuit arrange? thefspecific The subscribers` stations are of thetype usu.- ally employed in automatic telephonesystems and each includes a dial forusefin 4obtaining connection with any `other' station. The. linender, selector and connector switches are of the well known two-motion Strowger type. For a description of` the general structure of such switches, vreference `maybe lhad to pages 53 to cation representa telephone system in which VK5 `the invention is embodied, but the inventionis e5 inclusive ,of the 2nd eaitianlof Automatic y Telephony. yby Smith andCampbell. 'I'he selecf tor switch Si shown inrFig. 1 differsfrom the selector switch described in Automatic Telephony by the laddition of contacts operated by kthe 'double dog 3| while either of the vertical or rotary lholding pawls 32 or 33 is riding up on p A In the selector SI, the added contact springs 30 are actuated by the movement of the vertical holding pawl 32 vwhile the shaft is being stepped from-onelevel to the next, or bythe movement ofthe rotaryholdingpawl 33 while the shaft is `being ,rotatedl fromone position to the next.

The closing of contacts 30 insures the continued operation of the vertical-stepping ,magnetrv 26 so that thevertical-stepping pawl is held in engagement with the ratchet long enough to prevent overstepping. The connector Calso differs from the connector switchdescribed in..AutQ

\ matic Telephony by the additionof contactsf'lll operated by movement` of @the double dog. 1I

while eitherof `the vertical or rotary holding i5 pawls 'i2 or13 lis, ridingA up (in a tooth of the vertical or rotary ratchets.; The vertical-stepping magnet or rotary-stepping magnet -69 operation `and, permits the subscribers Kline to be of higherlresistance andto have a lower.y ing are each heldl operated by theclosure of,c'on

Cil

sulation resistance without causing switch failures. The circuit arrangements of the selector SI and the connector C are shown in full in the drawings and their operation will be set forth in detail. The line-finder switch is represented by the brushes and a single set of terminals, all associated apparatus having been omitted. Reference may .lmehadfto` my Patent No. 1,711,682 granted May` 7, l929 ,for a r description of the operation of a line-nder switch of theStrowger type. i

Assuming a call to have been originated at station A, and that the line I has been extended through the brushes of line-iinderLFI to the rst selector SI, aV circuit is closedior operating the line relay I5.' 'I'his circuit is` traced from battery through the lower winding of relay I5, lowermostback contact of relay I4, brush I2 of linefnder LFI, over oneconductor of line I!! and through the telephone at station A, back over the other conductor of line I0, through brush II of lineffinder LFI, upper-` mannen', Dial tone is transmitted `from trans former22 to the calling subscriber and `when the calling subscriber dials the first digit of the number Yof a station with which connection is desired, the linerrelay I5 vof selector SI is alternately releasedand reoperated as many times as there are units in the digit dialed` The first release of relay I5 closes `a circuit from battery through the winding -of the vertical-stepping magnet 28, winding of relay 25, lower front contact ofrelay I6; back contactvof relay I5,` and through theinner lowerfback contact of relay'I4 toground. VThe current yinthis circuit operates magnet 26 and operates Vrelay 25. The v'operation of magnet 26 steps the shaft and brushes-forselector SI up to the first level'of the, terminal bank. The reoperationA of relay I5 opens the above traced circuit through the Aoi? dial impulses by ,r'elay I5. ,slow releasing and remains operated until all `of lthe impulses',corresponding to the rst digit,

windings of magnet 26 Iand relay 25, but these windings are held energized through the front contact of relay and contacts 35, actuated by the movement oi the vertical holding pawl 32 'of double dog 3I while the shaft and brushes are being elevated, and through the back contact of release magnet 29, `over conductor I8 to ground at the inner lower back contact ofrrelay I4.` By holding the magnet 26 operated while the shaft is moving between levels, the vertical driving pawl (not shown) is heldin engagement with the vertical ratchet to prevent the shaft from being carried up by'its momentum `more 65 than one step in response to one dial impulse. When therholding pawl. 32 engages the ratchet to' hold tlfieshjaftA inits `first vertical off-normal position, thefcontacts are opened and the niagnet25 releases. Relayl is slow `in releasing and remains perated'during the receiving Relay 25 is valso haveibeen received. Each v,succeeding release and reoperation of relay I5 'is effective 1n slmlay 2l. reoperation of magnet 20 thereby advancing the ilar manner toA step up the shaft and brushes o f switch SI one step, overstepping being prevented by the closing of contacts 30 while each Vertical step is being taken.

As soon as the shaft of switch SI is moved out of normal position the vertical orf-normal springs 28 are actuated thereby disconnecting the battery potential through resistanceiZ'lfrom the test conductor Il. VWere the selector SI an intermediate selector instead of a rst selector, the

disconnection of this battery potential from conductor, I 'I` would render the selector SI nonselectable,` by a preceding selector, for use on another call. The actuation of the vertical offnormal springs 28 also closes a circuit for operating relay 2I this circuit is traced from battery throughresistance I9, back contact of the rotary-stepping magnet 28, winding of relay 2I,

f lower normally closed contacts of the 10th Ro-v tary step springs24, Amiddle contacts of the 'vertical off-normal springs 28, conductor I8, to

ground at the inner lower'back contact' of relay M., `,Tlie.release of relay 25, after thelast irnpulse `in the train created V`by, dialing Vof the first digit has been received, closes a circuit for 'operating the rotary stepping magnet 20; this: circuit is traced from battery through the wincl-4 ing of magnet 2U, upper front contactof relay 2|, back contactof relay 25," front contact of relay yI5 to ground' atnthe inner lower back contact `of relay I4. The operation of magnet 20 rotates` the brushes 4I, 42 and 43 into engagement with the rst set of terminals intheV level 'of the bank selectedin response to the vdialing of the iirst digit as above described.' The operationl oi nfiagnetv 20 also opens 'the operating circuit for relay 2I and connects the winding of relay fZI in series fwith the lower winding of relay .I4 to the test brush 43. If the terminal withfwhichtest brush 43 is in contact is not connected 'toan idle-,indicating potential, either on account of the test conductor of the trunk being open .or due to the .switch to which the trunk connects being oifnormal kor in use, relay 2I releases thereby causing the release of magnet 20. The release of magnet 20 disconnects the winding of relay 2I from the test brush 43and again closes'the operating circuit of re- The reoperation of relay 2I causes the brushesof selectorSvI tothe next set of terminals in the selected level. Relay 2I rand magnet 2G continue-their cycle of operation'suntil brush '43 encounters a test terminal which is connected 'to the idle-indicating potential or until the tenth and lastset of terminals inzthelevel is reached at whichl timethe actuation of the tlOth Rotary step. springs 24 prevents ,the reoperation of relay 2 I If the switch isrotated to the 10th rotary position and the test terminal of the tenth'set *ofy terminals is not connected tothe idle-indi- ;cating potential when brush 43 engages this terminal, the busy-,tone source 23 is connected `through the front lcontact of the springs 254,

the upper winding of relay I5, the uppermost back contact of relay4 I4, andi through brush il 1 of line-finder LFI toone of the conductors of linel. Y, When the test brush 43 encounters a terminal Vwhichis connected to the idle-indicating potenterminals in question to 4be,` connected to the connector switch C, the circuit for holding relay 2l operated, to prevent further `advance of the l should engage terminals connected kto the samev Vao 'facepiece l f 3 springs 6`8` Aor' 'switch C', over conductor' 5'I,

through fthetest terminal and brush VII'3 lower winding of relay I4', front contact of magnet 20,

Aw'iriding and lower front Contact of rela-y 2l, middlecontacts of the vertical off-normal springsv ,23, over conductor I8 to ground at the inner lower back contact of relay I4'. l Relay* vI4'fis suniciently energized by thecurrent through its lower winding to close its inner upper front contact and thus cause the complete operation of this relay` by energizing its upper winding.l If the brush of more thany one hunting selector trunk, the drop in potentialdue to the resistance `through` which the idle-indicating battery potential isconnected to the test terminals preventsy the operation of the test relay in any of these selector-s, thereby preventing a double connec tion. Should the test conductor connected to any set of terminals to which the brushes of switch SI are advancedl be open, relay 'IB can not be operated and the release of relay 2| causes the advance of the switch to the nent set of terminals. With relay I4 operated, a temporary busy-indicating ground potential is connected from the upper front contacto-f relay I5, overk lconductor I'I, through the middle upper front contact of relay Iliand'brush 43 tothe test f number is dialed,l relay 5 9 vis again alternately terminal of vtlnegseized trunk'. The operation of relay Ma'also causesthe release of relays'2I,I 5

and I6 and the release of magnet 20. The line Illis now connected through brushes II and I2 of line-nder LFLthe outermost front contacts of relay I 4, through brushes 4I and 42 to the windings of line relay 59 of -connector C. Re-y lay 59 operatesthereby causing the'operation of relay 6 0. Relay 55 connects 'a busy-indicating and holding rgroundpotential through its uppermost front Contact, over conductor 51 to the test terminal with whichbrushili or selectorSI is in contactto holdrelay I4 operated.' This holding potential is further extended 'through' thev "middle upper front Contact of relay I4 and brush I3 of line-:finder LFI to hold the cut-off relay (not shown) of line II! in well kno-wnmanner.

When the subscriber at station A dialsthe next to the last digit of the number of the subscribers station with which connection is desired, relay 5911s alternately releasedand reoperated in response to each of the dial impulses thus created.

The i'rst release of relay 59 closesacircuit-from ground at its upper back contact, through the inner upper front contact of relay BU, upper normally closed contacts of theverticalv off-normal springs 68, through the winding of relay 64 and winding of the verticalestepping magnet 65 to battery. Relayld and magnet 65 both operate, the 'operation of` magnet 65 being effective. to step the shaft and brushes of the connector gswitch C* upto the rst level of the terminal bank. j The vertical oil-normal springs 68 are actuated as soon 'as the shaft is moved out ofrnorrnal position, the circuit `for operating magnet 595 and relay 64 being thereby changed toz include the inner 4contact of relay 64 andthe lower frontcontact of l the vertical 'off-normal springs "6B, The; actuation of the vertical foi-normalsprings B3 also disconnects thel idle-indicating battery potential from testl conductor 5l to prevent seizure of the connector 'Cv by any other hunting selector until p after the switch C hasb'een restored to normal. The reloper'at'ion o'f relay 59 at theend 'of the rst dial impulse ofthe train causes thev release of magnet 65' unless the first impulse is not Sulli-v cientl-y longtoinsure proper switch operation, in

whichcas the magnet65 and relay S4 are held operated'bythe current ina circuit traced through the' front contact of relay alower front contact of the vertical off-normal lsprings '58,

inner upper riront contact of relay lowerrnost.

front contacteer relay 54, contacts IIJ closed by vthe actuation of the doublek dog 'll while 'the shaft is moving between normal andthe rstA level, to

ground at the back contact of release magnet'l.

Vll'ach succeeding releaseand reoperation of relay the actuation of the double dog 'l I, while the shaft is beingstepped fromeachlevel to the next, mantans` the energization of magnet 65 in response to each release of relay 55 for a sufficient lengthr `or time to prevent overstepping. Relay 6l) vis slow in releasing and remains operated during the receipt of dial impulses by relay 59. g Relay F54 isalso slow inreleasi'ng and does not release until all of the impulses created by the dialing of.the-next to the last digit of -the called subscribers number have been received byl relay 59. 'When the last digit of the called subscribers released and reoperated by each of the dial impulses thus created. The release of relay 59 in responseto the first of these impulses closes circuits for operating relay 53 and the rotary step- 'ping magnet 59; these vcircuits are traced from ground at the back contact of relay 59, inner upper front contact of relay 6ll, lowe`r front contact of the vertical oli-normal springs 68, back contact of relayll, lower back Contactv of vrelay 62, thence through the winding of relay G3 to l battery and through the4 upper backcontact yof relay 53 and the winding of magnet `r59`t'o battery. TheV operation of Vmagnetl E59 steps the brushes 8l, 32 and 33 into vengagement with the iirst set of terminals in the selected level. The

operation of relay 63 connects the winding of relay 62, in series with the inner'lower back contact `of relay 53,`th rough ythe upper iront contact of re'f ay E3 tothe-test brush 83; The reoperation of relay '5d at the end oi?` the first impulse opens the operating circuit for' magnet 59, but magnet. $55v is held operated while the shaft is moving from one rotary position tothe next by the closing of a holding circuit through contacts 'IIJ due to their (actuation by the double dog ll; this holding circuit is traced from' ground atl the back kcontact of release magnet lil,l through `contacts ld, lowermost viront ycontact of relay 63," to the inner upper yfront contactof relay' Ell, and thenceto `the windings of vrelay G3. and magnet 69 vas hereinbefore described. ',The continued operation of magnet 65 by the circuit through `contacts IQ insures against4 rotary overstepping. Relay '53 is slow in releasing andA remains opern ated runtil all-.of the impulses corresponding to theA last digit or the called number have vbeen received by relay 5S. Since the inner lower front Contact of relay 63 is inV parallel with the lower back contactof relay 52, a temporary operation of test relay @2 uponpassingover abusy terminal does not interfere with the operation of magnet 59 in response to succeeding impulses received by relay 59.-l `Each yrelease and reoperation of relay 59 is, therefore, elfective to cause the operation and release of magnet 69 and thus advance the brushes of the connector into engagement `with the set of terminals to which the called line is connected. If this line 'is busy, test `relay. `62is `operated due to the energizationof its winding when brush .83 cornes to rest on the grounded test terminal of the line; when relay63 releases, relay` 02 is held operated through the inner upper back Contact of relay 53 and the inner upper front contact of relay 62Y-over conductor 51 to ground at reupper winding of relay 53, uppermost back con tact of relay 63, brush 83 and test terminal, and

through the winding of the cut-offv relay (not shown) of the called line to battery. Relay 53 is suiciently energized by the current through its upper winding to close its inner lower front contact and thus cause the complete operation of this relay by the energization of its lower winding. Relay 53 closes the ringing circuit from the generator 52, through the middle upper front contact of relay 53, lower winding and lower back contact of relay 5|, lowermost front Contact of relay 53, brush 82, over the lower conductor of the called line 99 through the ringer (not shown) at station B, back over the other conductor of line 99, brush 8|, uppermost front contact of relay 53, to ground at the uppermost back Contact of relay 5|. Ringing tone is transmitted throughcondenser 55 to the calling station. When the receiver is removed at station B, relay 5| is sufficiently energized by the current through itslower winding to close its inner upper front contact and thus cause the complete opere ation of this relay due to the energization of its upper winding. Relay 5| completes the talking connection through its outermost front contacts and through condensers 50, talking current being supplied to the called station through the windings of relay 58. The operation of relay 58 while the line is closed at station B interchanges the connection between the calling line and the windings of relay 59, the resulting reversal of current being useful for supervision or call charging.

When the calling subscriber replaces the receiver on the receiver hook, relay 59 releases followed by the release ofrelay 6B. The release of relay 59 causes a momentary operation of relay 63 before relay 60 releases. The release of relay 60 is followed by the release of relay 53 and the connection of conductor 51 through the upper back contact of relay 62, upper windingv of relay 53, uppermost back contact of relay 53, to ground` at the inner upper front contact of relay 53 as a guarding potential in place of the ground previously furnished atthe uppermost front contact of relay 90. While relay 63 is operated after relay '59 releases, the sleeve conductor 51 is momentarily freed of any ground potential, thereby causing the release of relay I4 of selector Sl and the release and return to normal of the lineiinder LFI. The release ofrelay` I4 closes la circuit for operating the release magnet 29, and the brushes of switch SI are restored to normal. The release magnet 29 is held operated until the vertical off-normal springsare restored to normal position. the holding circuit being traced from the winding of magnet 29, through .the llower front contact of the vertical oir-normalA springs '28, front contact of magnet 29, over conductor I8,

to groundat the inner lower back contact of relay I4. 'VWhen the shaft reaches normal and springs,

to cause the operation of -a trouble alarm signal.

When the receiver is replaced on the receiver hook at the called station, relay 58 releases iollowed by the release of relays 5| and 53. With relays 59,169 and 53 all released,.the release magnet 91 is operated. Magnet 61 locks through'the `upper front contact of the vertical oir-normal springs 98. When the shaft reaches normal, magnet 01-releases and the idle-indicating battery-potentialisagain connected through resistance 15 to the sleeve conductor 51 thereby rendering the connector C selectable for use on another call.

v In Fig.,2 is sho-wn an alternative arrangement of a selector for insuring against double connections. Upon extension'of a calling line through the line-nder LFZ to theselector S2, the line relay' ||5 is operatedin series with the calling line. The operation of relay |,|5 causes the operation of relay H6. Relay IIB connects ground to the sleeve conductor 1 to hold the line-lnder LF2 and cut-off relay (notlshown) of the calling line. l/Vhen the calling subscriber dials the first digit ,ofk the number of a subscribers station with which connection is desired, relay |5 is alternately released and reoperated,.relay |25 and Vthe vertical-stepping magnet |26 being operated in series upon the release of relay. I5 in response to the first dial impulse. Magnet |26 releases when relay ||5 reoperates, each succeeding release and reoperation of relay ||5 being effective to cause a corresponding operation and release of magnet |26. YRelay |25 is slow in releasing and remains operateduntil relay ||5 reoperates after the ylastl of the train of impulses has been received. Relay ||6 is also slow in releasing and i -is operatively unalected by the receipt of dial impulses. Each operationof magnet |25 raises the brushes IM, |42 and |43 one step, thereby .steppingrnagnet |20, lower normally closed contacts of the 11th Rotary step springs |24, middle contacts of the vertical off-normal springs lower back contactof relay ||4. When relay |25 releases, after all of the impulses created by the dialingof the rst digit have been received, a circuit is closed for operating' the rotary-stepping magnet |20; vthis circuit is traced from battery through the Winding of magnet |20, front contact of relay |2|, lback contact of L relay |25, and through the front contact of relay- I5 to ground iat the innery lower back contact of relay I4. The

`e5 |28, over conductor ||8,A to ground at the inner' the/,b ushes are rotated .tothe f llth rotary posi.

tion, Hinwhichposition lthe vllthRotary step y l and I42'to the selectedtrunk.` Relays H5 and I I6 release but relay I I4 is held through its upper n test terminal j d tor leading i eneretien ef magnet mV steps ,the bushes inte;

eeeeeemetwitll .t1-,1e @ret l selected level and causes the The. release ef reley .lil ,eeueee the. .release ef magnet-120, Upon release of relay I .2I, a testing connection isclosed from groundfat theripper;`

et of ,ter in 'ls lin the` most front Contact of relay vIIS,tflfirough the lower Winding of relay IM, upperv winding andl b aclv-contact `of relay IE5, through brush Ult ltothe., `set with which-the brushes f are in engagement. Y T ,f thefsugceedingswitch tor of me which this set of terminals isonrreCted is ,busy, in which case guarding ground potentialfonif the test confcurrent through the lower winding of relay II4 and upperr Winding of relay I2I; and relay 12| is reoperated. due tothe current through its lower winding and the backcontactlof magnet 52), soy

that magnet 'n IZQII` andrelay I ZLcontinueftheir cyc-l'efof operations to step the brushes from one terminal to the nentuntil'brush N3 encounters a testterminal connected fto batterytpotential as` anidle-indicatingScondition. If allr of r the terminals in the selected levelr are non-selectabla springs I2 4 areY actuated to prevent further 4opt- ;ration of thev stepping relay 'I2,I `and a busy teneis transmittedto .thevcalling Aline.

When `brush M3 Yencountersthe idle-indicating battery potential, vthe cut-through YrelayHIIlis operated sufciently byf-the .current through its lower winding to close its inner upperirozntcorn vtact- 'a nc l tflnivsn causethe complete operation of this relay due to the current through, its upper winding, but the stepping relay I2! can not reoperate since the current throughits upper winding electromagnetically opposes the current through its lower winding. If the brushes of two selectors should simultaneously engage terminals connectingk to the same trunk, the resistance in series with the idle-indicating potential source is suicient to prevent the operation of the cutthrough relay of either of these selectors and to permit the operation ,of the stepping relay ,in each of the selectors and thus preventa double connection. The operation of relay IM extends the connection from the calling line through its outermost front contacts and through brushes IM winding over sleeve conductor II'I through brush |43 to ground potential supplied by the succeeding switch in well known manner. When the connection is released by the calling subscriber this ground potential is disconnected from ltheterminal with which brush |43 is in contactr and relay H4 releases. .The release of relay IIA completes the usual circuit for operating the release magnet IZB and thebrushes and shaft Aof switch S2 are thereupon returned tonormal posi comprising a shaft, a bank of terminals, a set the test terminal is eonnectedto a Y te this Switch is epee; there ie 11er `terr'ninal of thefset towhich the trunk isf,

the operation ef brushes meewegen 'Seid eheft en@ mera-ele ther Vith, Iinto operative engagefrnent pping magnet, a drivingwpawl forf! operante@ .een gage, sa

eeev brushes eee] eter; et e weer "end e retaining pawl for holding said i shaft vin advancedposirfY tion,` an .impulse receiving relay, a circuit closed Krelatieleeeenee-te eeeh; impulse received Vforr operating said stepping. margriet, .and 3f QTCJJCIQSC bythe release f said d .weer es Seid shaft i begins te edrenee eut lef eneeeeitie'n eed until Y.

for maintaining 2f 1D" lector Co nprising ha, shaft, a ban k. `ofy termin l e Set ef breelheemeentee en Seideheft emmer-.l able therewith into cooperative engagement withy saidl terminals, anda'steppingA magnet, `the o per-VVA Seid meeee heine effeeiire teaedveneef thebrushes one step at a time, trunksl connected` ation of tothe terminals of said banlgthe idle condition of a trunk being indicated by ab'attery Vpotential connected over its sleeve conductor to the test nected, means including a` st pping relayand said magnet `for switching one ofA said trunks, a test circuit closed wl en the testbmsh is in yengagement ennuie-.test

trunk, .which circuit includesah winding of saidlswi'tching relay andawin'din of`v` termin Il of a Seid; Stepeieereler f 3. In a step-,byystep selectorswit the 4,energization 'offk saidmagnet. i telephone system, i a step-by-stepl se?,v

of said magnetbeing effective to l cooperationfwith a1 ratchetfon f said shaftsv the y nragnet being effective to enf. id pawl and ratchet to .advance the shaft advancingv saidf-r ;l o rusl'1es; at i relay for l operation to` seize an idle move said switchv one step, a circuit for operating `said magnet, an impulse circuit, means forclosing said operating circuit in response to .an ,imf'

pulse in vsaidirnpulse circuit, another circuit for energizing said magnet, andsprings actuated upon each step of said `switch for closing and maintaining said other circuit until said switch V has stepped. n

Ll. In a step-by-step selector switch, a magnet, the operation of said magnet being effective to rmove said switch one step, a circuit for ,operatev ing said magnet, an impulse circuit, means for closing said operating circuit in response to the opening of said impulse circuit, another circuit forenergiaing saidv magnet, and springs actuated upon each step of*` said switch for closing and maintaining said other circuit until said .switch has stepped.

5. In a numerical step-by-step selector switch, a steppingk magnet, an impulse circuit, -means responsive to an impulse in said circuit' for'operating said magnet to advance the switch one step, and springs actuated'by the retaining pawl 'while sliding over a toothvof the ratcheton the switch shaft for maintaining the energization of said stepping magnet until the step has been l completed.

6. In a numerical"step-by-step switch, a vertical-stepping magnet and operating circuit therefor, a rotary-stepping 'magnet and operating circuit therefor, ia rdouble dogengaging the vertical and rotaryV ratchets on the shaft of said switch for maintaining the shaft in an-oiI-normal position, van impulse circuit, means responsiveto an impulse in said impulse circuit for closing the operating circuit of said verticalsteppingmagnet, means responsive to another impulse ,in said impulse circuit for closing the operating circuitof said rotary-stepping magnet,

another circuit for energizing said vertical-step-v ping magnet, another circuit for energizing said rotary-stepping magnet, and contact springs actuated by the movement of said double dog while the shaft is being moved one vertical step for closing said other circuit for energizing the vertical-stepping magnet and actuated bythe movement of the double dog while said shaft is being moved one rotary step for closing said other circuit for energizing the `rotary-stepping magnet.

A7. In a step-by-step selector comprising a bank'` of terminals, aset of brushes and a stepping mag-v net, trunks connected tothe terminals of4 said bank, the idle condition ofY a trunk being indcated bya battery potential connected over its sleeve conductor to the test terminal of the set to which theV trunk is connected, means including a stepping relay andsaid magnet for advancing said brushes one step at a time, aswitching relay, and a circuit for operating 'said switching relay and for preventing the Vreoperaticmy of said stepping relay when the brushes encounter the terminals of an idle 8. In a step-by-step selector comprising a bank i of terminals, a set of brushes and a stepping magnet, trunks connected tov the terminals of said bank, theidle condition of a trunk being indi? the terminals of anidle trunk, said circuit including fthe winding of said stepping relay and a front contact of said magnet. s

19. In a step-by-step selector comprising a bank of terminals, a set of brushes and a stepping magnet, trunks connected 4to the terminals of said bank, the idle condition of a trunk being indicated by a battery potential connected over its sleeve conductor to the test terminal of the set to which the trunk is connected, kmeans including a stepping relay and said magnet for advancing said brushes one ystep at a time, a switching relay, and a' circuit for operating said switching relay and for holding said stepping relay when the brushes encounterA the terminals of an idle trunk. Y

10. In a step-by-step selector comprising a bank of terminals, a. set of brushes and a stepping magnet, trunksconnected to the terminals of said bank, the idle condition of a trunk being indicated by a battery'potential connected over its sleeve conductor to the test terminal of the set to which the trunk is connected, Ameans including ajstepping delay and said magnet for advancing said brushes one step at a time, a switching relay, anoperating circuit for` said stepping relay including one winding of'said stepping relay anda back contactof said magnet, and a circuit including another Winding and a back` contact of said stepping relay for operating said switching relay to seize an idle trunk, Vthe current through said other winding of said stepping relay being electro-` magnetically opposed to the current through said one winding.

; HENRY HOVLAND. 

